The present invention relates to hydrogen-permeable membranes, which separate hydrogen from mixtures of gases by allowing selective diffusion of hydrogen through the membrane while substantially blocking the diffusion of other components in the gas mixtures. In addition, this invention relates to methods of producing dense hydrogen-permeable membranes, methods of mechanically supporting thin hydrogen-permeable films and methods of re-enforcing membrane materials which are embrittled by hydrogen. The invention also relates to membrane reactors for hydrogen separation employing the membranes of this invention and to methods for separating hydrogen using these membranes.
Hydrogen can serve as a clean fuel for powering many devices ranging from large turbine engines in integrated gasification combined cycle electric power plants, to small fuel cells. Hydrogen can also power automobiles, ships and submarines and can be used as heating fuel. Large quantities of hydrogen are used in petroleum refining. In chemical industry, membranes, which are selectively permeable to hydrogen are expected to be useful in the purification of hydrogen and also to shift chemical equilibrium in hydrogenation or de-hydrogenation reactions or in the water-gas shift reaction. Membranes are used by the semiconductor industry for production of ultra-high purity hydrogen. The nuclear industry uses membranes for separation of hydrogen isotopes from isotopes of helium and other components of plasmas.
Methods of producing hydrogen include steam reforming or partial oxidation of natural gas, petroleum, coal, biomass, and municipal waste. Production of hydrogen from these sources is accompanied by production of carbon dioxide, carbon monoxide, and other gases. It is highly desired to separate hydrogen from the unwanted side-products and gaseous contaminants. Use of hydrogen permeable membranes is one means for separating hydrogen from complex gas mixtures.
U.S. Pat. No. 2,824,620 (de Rossett) relates to hydrogen-permeable membranes formed from a layer or film of hydrogen-permeable membrane on certain porous support matrices. In related U.S. Pat. No. 2,958,391 (de Rosset) the hydrogen-permeable membrane is formed using a support matrix of sintered metal particles. U.S. Pat. No. 3,350,846 (Makrides, et al.) reports hydrogen-permeable membranes formed from Group VB metal foils coated on both sides with palladium catalysts.
U.S. Pat. No. 4,536,196 (Harris) relates to a hydrogen diffusion membrane which is palladium or a palladium alloy coated with at least one metal selected from Group IB, IVB, VB and VIB of the Periodic Table. The coating is reported to increase resistance of the palladium or palladium alloy to poisoning. U.S. Pat. No. 4,313,013 (Harris) relates to a hydrogen diffusion membrane of palladium or certain palladium alloys that has been treated with silane and/or silicon tetrafluoride. The treatment is reported to deposit a film of elemental silicon to prevent poisoning of the metal or alloy and extend its use before regeneration is required.
U.S. Pat. No. 4,468,235 (Hill) relates to separation of hydrogen from other fluids employing a hydrogen-permeable coated alloy at a temperature between about 100-500° C. The alloy reported is a titanium alloy comprising 13% by weight vanadium, 11% by weight chromium and 3% by weight aluminum stabilized in the body-centered cubic crystalline form. At least one surface of the alloy is coated with a metal or alloy “based on” palladium, nickel, cobalt, iron, vanadium, niobium, or tantalum.
U.S. Pat. No. 4,496,373 relates to a hydrogen diffusion membrane that is a non-porous hydrogen-permeable metallic membrane provided with a coating of an alloy of palladium with at least 45 atomic % Cu or at least 50 atomic % Ag or at least 7 atomic % Y. The membrane contains Cu, Ag or Y in a concentration at least equilibrated with the coating at operational temperature.
U.S. Pat. No. 4,589,891, Iniotakis et al., reports hydrogen-permeable membranes formed by galvanic deposition of metals with high hydrogen permeability onto fine mesh metal fabric. High permeability metals are said to include Nb, Ta, V, Pd and Zr. Palladium and its alloys are said to be preferred because they are resistant to the formation of hydrides and to surface oxidation. A thin metal layer, 1 to 20 microns thick, particularly of palladium and palladium silver alloys is formed on fine metal wire mesh. The metal of the wire mesh is not specified. The patent also reports membranes formed by thin layers of hydrogen-permeable metal sandwiched between two fine metal mesh screens which provide mechanical support. The authors reported that fine metal mesh were superior to porous metals as mechanical supports for thin films of palladium and palladium alloys. Related U.S. Pat. No. 4,699,637, Iniotakis et al., reports hydrogen-permeable membranes formed by sandwiching a layer or foil of a hydrogen-permeable metal between two fine metal meshes to provide mechanical support.
U.S. Pat. No. 5,738,708, Peachey, et al., reports a composite metal membrane for hydrogen separation in which a layer of Group IVB metals or Group VB metals is sandwiched between two layers of an oriented metal layer of palladium, platinum or alloys thereof. The oriented metal layer is referred to as the “catalyst” layer. The membrane is exemplified by one formed by metal evaporation (Pd) onto a tantalum foil. Additionally, optional buffer layers of certain oxides and sulfides are reported to reduce interdiffusion of the metals. Related U.S. Pat. No. 6,214,090 (Dye and Snow) reports that palladium, platinum, nickel, rhodium, iridium, cobalt and alloys thereof can be used as the outermost catalytic layers of the hydrogen transport membrane. They also report the use of a diffusion barrier which includes non-continuous layers of metal chalcogenides between the core metal and catalyst layers.
U.S. Pat. No. 5,149,420 (Buxbaum and Hsu) reports methods for plating Group IV and VB metals, in particular niobium, vanadium, zirconium, titanium and tantalum, with palladium from aqueous solution to form membranes for hydrogen extraction. The metal to be plated is first roughened and electrolytically hydrided before plating. Related U.S. Pat. No. 5,215,729 (Buxbaum) reports a membrane for hydrogen extraction consisting essentially of a thick first layer of refractory metal or alloy that is permeable to hydrogen and a second layer coated over the first layer consisting essentially of palladium, alloys of palladium, or platinum. Refractory metals are said to include vanadium, tantalum, zirconium, niobium and alloys including alloys said to be non-hydrogen embrittling. Alloys specifically stated in the patent to be non-hydrogen embrittling are: “Nb 1% Zr,” “Nb 10 Hf 1 Ti,” Vanstar(Trademark) and “V15Cr5Ti.”
U.S. Pat. No. 5,931,987 (Buxbaum) reports an apparatus for extracting hydrogen from fluid streams containing hydrogen which has at least one extraction membrane. The patent also reports an extraction membrane consisting essentially of a layer of Pd—Ag or Pd—Cu alloy or combinations thereof one of the surfaces of which is coated with a layer consisting essentially of palladium, platinum, rhodium and palladium alloys. U.S. Pat. No. 6,183,543, which is a continuation-in-part of U.S. Pat. No. 5,931,987(Buxbaum) also relates to an apparatus for extracting a gas, particularly hydrogen, from a fluid stream using plate membranes. The patent reports that extraction membranes can have a substrate layer of certain specified alloys: Ta—W, V—Co, V—Pd, V—Au, V—Cu, V—Al, Nb—Ag, Nb—Au, Nb—Pt, Nb—Pd, V—Ni—Co, V—Ni—Pd, V—Nb—Pt or V—Pd—Au with an outer catalyst layer of palladium, platinum, rhodium and palladium alloy. Preferred outer catalysts were stated to include Pd—Ag alloys with compositions between Pd-20% Ag and Pd-50% Ag, alloys of Pd-40% Cu, and Pd-10% Pt.
U.S. Pat. Nos. 5,139,541; 5,217,506; 5,259,870; 5,393,325; and 5,498,278 (all of Edlund) relate to non-porous hydrogen-permeable composite metal membranes containing an intermetallic diffusion barrier separating a hydrogen-permeable base metal and a hydrogen-permeable coating metal. In U.S. Pat. Nos. 5,139,541 and 5,217,506 the intermetallic diffusion barrier is described as a thermally stable inorganic proton conductor. A proton conductor is broadly defined therein to include H+ ion conducting materials and any material that shows complex ion motion at high temperatures such as the oxides and sulfides of molybdenum, silicon, tungsten and vanadium. In U.S. Pat. No. 5,217,506, specific uses for the hydrogen transport membranes which include decomposition of hydrogen sulfide and extraction of hydrogen from a water-gas shift mixture of gases are discussed. U.S. Pat. No. 5,259,870 reports the use of oxides of aluminum, lanthanum and yttrium as the diffusion barriers. U.S. Pat. No. 5,393,325 reports a composite metal membrane in which an intermediate layer is positioned between the base metal and a coating metal which intermediate layer does not form a thermodynamically stable hydrogen impermeable layer at temperatures ranging from about 400° C. to about 1000° C. The intermediate layer is said not to be a pure metal or metal alloy. The base metal is said to be selected from the metals of Group IB, IIIB, IVB, VB, VIIB and VIIIB and hydrogen-permeable lanthanides and alloys. The intermediate layer is said to include not only various oxides and sulfides, but also carbides, nitrides, borides, fluorides, zeolites, graphite and diamond.
U.S. Pat. No. 5,498,278 (also of Edlund) reports the use of a flexible porous intermediate layer between a rigid support layer and a nonporous hydrogen-permeable metal coating layer or the use of a textured metal coating layer to form a composite hydrogen-permeable inorganic membrane. The support layer is said to include a wide range of materials including “dense hydrogen-permeable metals, porous, perforated and slotted metals,” and “porous, perforated and slotted ceramics.” It is stated that it is key to accommodating dimensional change that a flexible non-sintered intermediate layer be provided or that a textural coating layer be employed. The intermediate layer is also said to prevent intermetallic diffusion between the support matrix and the coating metal layer. In all of the Edlund patents, interdiffusion between the base metal layer and the coating layer is mentioned as a problem that is solved by introduction of the intermetallic diffusion barrier or the intermediate layer. This implies that the coating layer and the support or base layer of the membrane would be made of different materials. These patents do not teach or suggest the use of base metal layers and coating layers made of the same metals to eliminate metallic interdiffusion problems. Ceramic monoliths with honeycomb-like cross section are also reported as supports for coating layers.
The scientific literature relating to hydrogen transport membranes is extensive, especially concerning membranes of palladium and it alloys, some of which are available commercially. However, the prior art does not attempt to lattice match the metal membrane material with the material of the mechanical support. In specific embodiments of this invention, lattice matching is used to minimize interfacial strain and membrane failure due to initiation of cracks and provide improved hydrogen-permeable membranes.